This commit implements the core FocusStreamer application with the following features:

Backend (Go):
- X11 window detection and focus tracking
- HTTP API server with REST endpoints
- Application whitelist management
- Pattern-based auto-whitelisting using regex
- Configuration persistence to ~/.config/focusstreamer/config.json
- WebSocket support for real-time window updates

Frontend (React + Vite):
- Modern web UI for application management
- Real-time display of currently focused window
- Application list with whitelist toggle
- Pattern matching configuration
- Responsive design with professional styling

Project Structure:
- cmd/server: Main application entry point
- internal/api: HTTP API server implementation
- internal/config: Configuration and data models
- internal/window: X11 window management
- web/: React frontend with Vite

Documentation:
- ARCHITECTURE.md: Detailed architecture and design
- README.md: Quick start and usage guide
- TESTING.md: Comprehensive testing guide
- CONTRIBUTING.md: Development and contribution guidelines
- Makefile: Build and development commands

Features:
- Detect running applications via X11
- Track focused window in real-time
- Whitelist specific applications
- Use regex patterns for auto-whitelisting
- Persistent configuration
- REST API for integration
- Modern web UI for configuration

Future enhancements:
- Virtual display creation
- Window capture and composition
- Wayland support
- Cross-platform support